It seems Mediterranean peoples were weakened by a severe multi-year drought. A handful people (the so called mysterious sea people) with different military strategy overrun multiple bronze age states.

Trade collapse led to impossibility of making bronze weapons, which further amplified collapse. This was possible because tin mines were few and far apart. So it was a vicious cycle triggered by a weak point, on a background of hardship. The lesson is not to depend on a single failure point.